The overall objectives of the project are concerned with the elucidation of the role of different states of arousal, attention, associative learning, and pharmacological intervention in the transmission and processing of stimulus information in the somatosensory system of the monkey. To this end, single neuron activity is recorded from the hand representation of somatosensory area I of primates while in five types of behavioral situations: 1) the animal is simply seated in a primate chair while stimuli are applied to the receptive field of his hand; 2) the animal is placed in a soundproof room and allowed to fall asleep; 3) the monkey performs a simple go no-go behavior task for a fruit juice reward; stimuli have no cue value; 4) a conditions negative variation paradigm in which the cutaneous stimuli serve as behaviorally neutral test probes; 5) stimulus discrimination paradigm in which the direction of moving cutaneous stimuli indicates reward availability. The driven and spontaneous neural activity are recorded and analyzed quantitatively for their statistical properties. The experiments will help characterize the changes that occur in the neural encoding of a stimulus during states of arousal and slow wave sleep on the one hand, and associative learning and attention on the other. The other aspect of this study is to examine the effects of various psychoactive drugs on the encoding of stimuli in S-I and to change the arousal level of the animal by pharmacological means, thereby comparing the natural states of arousal and sleep with those of the drug induced states.